In the field of modern architecture, gypsum (main component being calcium sulfate dihydrate) is a major material used in the construction industry. Examples include a gypsum board for forming the ceilings and walls in a building, and conventional mortar for producing a finished surface on the internal ceilings/walls.
During the preparation of gypsum products, a mixture of calcined gypsum (calcium sulfate hemihydrate and/or anhydrous calcium sulfate) and water is cast, where the calcined gypsum (plaster) is hydrated by water to form a solidified gypsum which comprises crystalline hydrated gypsum matrix (calcium sulfate dihydrate), so that the gypsum products have high structural strength. Thus, the gypsum product has advantages of light weight and high strength and so is widely used in building products.
However, if the gypsum product is under conditions of high humidity for a long time, deformation behavior can occur, at times referred to as sagging or humidified deflection in the industry. Gypsum products that show this deformation behavior will present poor aesthetics after installation and will require expensive remediation work to correct. Therefore, how to overcome the poor deformation behavior of solidified gypsum has been the focus of study in the field of construction, and some achievements have been made.
For example, Chinese patent publication No. CN101747014A discloses a method to improve the anti-sagging of the gypsum product by adding boric acid as additives into the calcined gypsum. U.K. patent GB1481788A discloses using Gallic acid as anti-sagging additive in order to improve anti-sagging of a gypsum board. U.K. patent GB 1226333A discloses that precast gypsum plaster sheets, slabs and blocks containing tartaric acid have a greater resistance to plastic flow than similar articles not containing tartaric acid. It is also known that phosphates can be used as disclosed in U.S. Pat. No. 6,342,284.